BuddyPress.org

In terms of privacy of seeing profiles, this is coming in a later version by default, but for now, you can do what I proposed at the following:

https://buddypress.org/forums/topic.php?id=160

It just makes the entire buddypress-member theme from being no viewable by anyone but logged in members. The buddypress-home theme still is available for signups though.

Trent